Apparatus and method for determining the wear condition of a chain

ABSTRACT

In a method for determining the elongation of segments of a chain of a chain drive during operation, a plurality of measured values is determined at different positions of the chain. A plurality of length values is determined from the plurality of measured values and the length values are assigned to the segments of the chain, with the length of the segments of the chain being smaller than the length of the chain.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of German Patent Application,Serial No. 10 2017 119 300.6, filed Aug. 23, 2017, pursuant to 35 U.S.C.119(a)-(d), the disclosure of which is incorporated herein by referencein its entirety as if fully set forth herein.

This is one of two applications both filed on the same day. Bothapplications deal with related inventions. They are commonly owned andhave the same inventive entity. Both applications are unique, butincorporate the other by reference. Accordingly, the following U.S.patent application is hereby expressly incorporated by reference:“APPARATUS AND METHOD FOR DETERMINING THE WEAR CONDITION OF A CHAIN”,Ser. No. 16/109,180.

BACKGROUND OF THE INVENTION

The present invention relates to a method for determining the elongationof chain segments of a chain drive, a sensor device for determining theelongation of chain segments as well as a chain and a computer programfor carrying out the method.

The following discussion of related art is provided to assist the readerin understanding the advantages of the invention, and is not to beconstrued as an admission that this related art is prior art to thisinvention.

Chain drives are used in a variety of industrial applications for driveor transportation purposes. Several chain strands are often used. Inaddition to a circulating chain that usually runs endlessly, a completechain drive includes several sprockets that serve to deflect the chain,as well as drive or transport elements that are connected to the chainand are activated by the chain. Due to the abrasion of parts in thechain joint that move relative to one another, a chain is subject towear during operation. Other factors, such as chain run-in elongation,stretching, bearing play and bearing wear, can also lead to chainelongation and ultimately to failure of the drive unit. Further factorsinfluencing chain wear are the forces acting on the chain and loads oralso external influences determined by the environment. Due to thecomplexity of these interrelationships, it is not possible to predictchain wear and thus possible malfunctioning during operation or evenfailure of the drive unit.

Complex chain drives are increasingly being used due to the everincreasing number of fully automated machines and systems required formodern factory automation. Due to the high investment costs for such ahigh degree of automation and global pricing pressure, it is necessaryto reduce machine and system downtime to an absolute minimum and tocompletely prevent unplanned downtime.

In addition to direct financial losses, unplanned downtime also leads toindirect problems, e.g. interruption of the logistics chain up todelivery times that cannot be met and thus to further financial losses.However, even slight wear and tear can lead to production errors due toprocesses synchronized by chain drives and these errors must then bereadjusted manually. Since the wear of a drive chain or its elongationcannot be avoided or predetermined, continuous monitoring of a chaindrive is indispensable in order to be able to carry out timelyinspections for adjusting the synchronized processes and replacingdefective chains.

The wear of a drive chain can be determined by measuring the force, thedistance or the angle of rotation of chain tensioners or two rotaryposition sensors at the drive wheel and at the load wheel. However, achain tensioner is not needed in all application scenarios and rotaryposition sensors cannot be used everywhere either. In addition, they arethen influenced by wear or chain elongation. However, such methods mustbe precisely adapted to the specific process, as the measurement inthese cases depends on the total chain length and also on the wear ofthe sprockets. Adjustments are very time consuming and error prone.Therefore, these methods are not generically applicable.

Depending on the sensors and measuring principle used, prior artapproaches have many shortcomings. Conventional measuring systems withfixed distances between sensors require a drive with a constant speedfor precise measurement of the chain elongation and result inmeasurement errors due to irregularities in the drive system, forexample relative slip between the drive wheel and the drive chain orwear of the sprockets. Optical sensors, on the other hand, are notsuitable for practical use in drive and transportation systems in manyapplications, as the industrial environmental conditions can lead tofailure or incorrect measurements of the optical sensors, especially dueto dust and dirt. In contrast, inductive sensors not only have aswitching sensitivity in the measuring direction but also an inherentswitching sensitivity perpendicular to it, so that inductive sensorshave a tendency not only to vibration sensitivity but also to falsemeasurements.

Common to all prior art approaches is that the chain elongation cannotbe traced back to the elongation of individual chain segments. In theevent of detected elongation, this means that the chain as a whole mustalways be replaced, which is associated with significantly higher costs.This additionally means that the limit values previously specified alsohave to take into account singularities in the chain elongation untilthe chain is replaced, thus requiring significantly lower limit valuesthan if the elongation of individual chain segments or even chain linkswere known. Although individual apparatuses and methods already allowfor the measurement of values that enable an elongation also for chainsegments, these values cannot be assigned to individual chain segmentsconsidered during a measurement, so that this in turn leads to thecomplete replacement of the chain.

It would therefore be desirable and advantageous to address prior artproblem and to obviate other prior art shortcomings.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a method fordetermining an elongation of segments of a chain of a chain drive duringoperation, includes recording a plurality of measured values atdifferent positions of the chain, determining a plurality of lengthvalues from the plurality of measured values, and assigning the specificlength values to the segments of the chain, respectively, wherein alength of the segments of the chain is smaller than a length of thechain.

Such a method makes it possible to determine the elongation ofindividual chain segments and also to assign it to the respective chainsegments. This means that the chain as a whole does not have to bereplaced, as with previously known methods for detecting supercriticalchain elongation. Furthermore, it is advantageous that the specifiedlimit values, which indicate a critical state of the chain or individualchain segments, do not have to consider singularities in the chainelongation, thereby enabling the use of significantly higher limitvalues, since the singularities of actual chain elongation can bedetected. Moreover, as a result of this method, it is no longernecessary to replace the entire chain if the limit value is exceeded.Rather, if the elongation of the individual chain segments or even chainlinks is known, only the chain segments or chain links that alsodemonstrate supercritical elongation need to be replaced. This not onlyleads to longer operational periods of the machine or system before thechain has to be serviced, the material costs for replacing the affectedchain segments are also significantly lower, which is associated withconsiderable cost savings.

To ensure clarity, it is necessary to establish the definition ofseveral important terms and expressions that will be used throughoutthis disclosure. The term chain segment relates to a chain section of apredefined length. During the process in accordance with the invention,a length value is determined for each chain segment. The chain segmentcan comprise one chain link but also several chain links andattachments. With regard to the attachments, it is not necessary for thechain segments to be identical.

In accordance with the present invention, the chain can be divided intoa large number of segments. These segments may overlap. Advantageously,however, they border each other. In both cases, however, they providecomplete coverage of at least those parts of the chain that areaccessible to the sensor for position or elongation measurements. Thelength or number of segments depends on the chain length.Advantageously, small segments are selected, since in the case ofsupercritical elongation only the affected segment has to be replacedand the defined limit values for critical elongation do not have toconsider averaging over a large number of chain links. At least 5segments, preferably at least 10 segments, are distributed over thelength of the chain. Currently preferred is the provision of at least 25segments. Optionally, a length of the segments can have a maximum of 25chain links, preferable are 10 chain links. Currently preferred is alength of the segments of 5 chain links.

According to another advantageous feature of the present invention, anumber of the segments can correspond to a number of chain links of thechain which are guided past one or more sensors as the measured valuesare recorded during operation. This has the advantage that eachindividual chain link can be monitored with regard to its elongation. Ifcritical elongation should occur in a single chain link or in only veryfew chain links, this elongation could remain undetected due to theaveraging of the measured values over a larger range. The limit value tobe set would have to take this into account and would therefore have tobe much smaller, which would lead to longer machine downtime andconsequently to higher costs.

According to another advantageous feature of the present invention, ameasurement for recording the measured values can be continuouslyrepeated during operation of the chain drive. For this purpose, themeasurements are repeated on successive chain segments. If a circulationor run of the chain segments to be monitored has ended, monitoring iscontinued segment by segment with the following circulation or run. Thishas the advantage that the subsequent assignment of the measured valuesor length values can be allocated to the individual segments moreeasily.

During the process, the measured values of the individual segments aredetermined first. Length values are determined from the measured valueswith the aid of a control unit. These length values are compared withreference values. The reference values can be limit values stored in thecontrol unit before measurement starts. The reference values can also bedetermined from a zero measurement carried out on the chain in itsoriginal state. For this purpose, it is necessary to define a maximumdeviation, on the basis of which it can then be specified which measuredor length values reach a corresponding error state.

A wide variety of different sensors may find application for carryingout this process. Therefore, measured values can be optical signals,magnetic signals or other signals. It is therefore possible to use alarge number of sensors to carry out this process.

In a further step of a method according to the present invention, theposition of the chain segments is recorded. Several optionalpossibilities are available for this. According to one advantageousembodiment of the present invention, the position of the chain can bedetermined via an additional sensor. This sensor can be designed todetect a structural change in the chain. The term “structural change” inthe chain can relate to any physical change in the chain or any changethat locally changes the physical property of the chain. All thesechanges can be detected directly or indirectly by a sensor. Thisincludes an additional strap mounted on a chain link or otherattachments that can be fixed to chain links. This list is only anexample and is not complete.

Optionally, the physical property of the chain is determined in order todetermine the position of the chain segments. With a local change in thephysical property of the chain, the position of the chain segments canbe determined by a sensor that is capable of detecting the local changein the physical property of the chain. When this component approachesthe sensor, the locally changed physical property is detected.

In an exemplary design of the invention, a component of the chain can bereplaced by a ferromagnetic component, resulting in a local change inthe magnetic field of the chain. When this component approaches a Hallsensor, the locally changed magnetic field of the chain is detected.Since the position of the replaced component is known, the position ofthe segments of the chain can be determined in this way. Optionally, thephysical properties of the chain can also be changed by components fixedto the chain. This can be done, for example, by an additional permanentmagnet fixed to a chain link.

According to another advantageous feature of the present invention, asequence of measured values or quantities determined from the measuredvalues, such as elongations of adjacent chain segments, can beinterrelated to determine the position of the chain segments. Acharacteristic pattern results from the sequence of measured values ordetermined variables. This is possible because the individual chainsegments and/or the individual chain links do not elongate evenly duringoperation. There are chain segments and/or chain links which are eithersubjected to more stress than others or have different mechanicalcharacteristics due to manufacturing tolerances, which lead to differentelongation of the individual chain segments and/or the individual chainlinks during long-term operation. This has the advantage that there isno need for a second sensor to determine the position of the chain andfor a structural change of the chain, which the second sensor can use todetermine the position of the chain. The infrastructure and capacitiesprovided for controlling and evaluating the measurement results can alsobe dispensed with. This significantly reduces the costs for the sensoraccording to the invention.

According to one advantageous feature of the present invention, thepattern of the sequence of elongation of the individual chain segmentsand/or the individual chain links can be described by a selection ofmeasured values or quantities determined from them. This selection canbe achieved by reducing the measured values or the determined variables.The measured values can be reduced by using only a selected number ofsegments and/or chain links in the chain to determine the position ofthe chain segments. Selection can optionally also take place byobserving a continuous section of segments and/or chain links, or by areduction in which only every second, third, fourth or x segment and/orchain link is observed. When a chain is monitored with several sensorsto record the measured values, the position of the chain segments can bedetermined by using only the segments and/or chain links that are passedby one of the sensors to determine the position.

According to another advantageous feature of the present invention, alocal significance can be determined from the measured values and/orfrom the variables determined from the measured values. Thissignificance can, for example, be a local or absolute maximum or minimumof the measured values or the variables determined from the measuredvalues. Significance can also be described in an alternative version byfurther characteristic curve features, such as turning points.

The term “local significance” within the scope of the present inventionrelates to a characteristic of the chain that can be detected by asensor. It is local because the chain position can be determined bydetecting the local significance, since the sensor for determining thelocal significance and the sensor for determining the length values ofthe individual chain segments and/or chain links are arranged at adefined distance from each other. Several local significances can bearranged on one chain. This is useful when the chains are very long,when the chains are not endless chains or when a reversal of directionis to be expected during operation. In such cases, it is advantageous tobe able to differentiate between the individual local significances sothat a clear assignment of the determined length values to therespective chain segments is possible. This can be achieved, forexample, because the local significances can be distinguished from eachother by the signals they detect, or by selecting different distancesbetween the local significances in a circulating endless chain, forexample.

According to another advantageous feature of the present invention, therelative position of local significances to each other is used todetermine the position of the chain. The relative position can bedescribed, for example, by the distance between two or more localsignificances. It is also possible to determine the distance betweenseveral pairs of local significances.

According to another advantageous feature of the present invention, thelocal significance can be determined from the sequence of measuredvalues or from the sequence of variables determined from the measuredvalues of several chain segments and/or the chain links. Optionally, anadaptation function can be determined from the sequence to determine thelocal significances. This adaptation function is determined from acorrection calculation based on a large number or all measured valuesand/or variables determined from the measured values.

According to one advantageous feature of the present invention, anoutput function containing trigonometric functional components and/orcomponents of a polynomial can be selected for the adaptation function.

According to one advantageous feature of the present invention, thelocal significance can include a structural change in the chain. Thisstructural change can be detected by a sensor. The position of thestructural change of the chain can be detected by a suitable sensorparallel to the recording of the measured values. A reference of thedetermined measured values to the respective chain segment or chain linkcan thus be established, since the determined measured values can beassigned to the respective chain segment or chain link via the detectedposition of the structural change and the number of chain segments orchain links passed after the detection of the structural change. Thestructural change of the chain can be, for example, an attachment fixedto a chain link. Optionally, the structural change of the chain can be astrap mounted on a chain link. As an alternative, the structural changecan be a permanent magnet that is fixed at a position of the chain. Bothdesigns can be detected by suitable sensors (optical or magnetic).Further structural changes in the chain which change the geometric orphysical properties of the chain are conceivable. Optionally, severalstructural changes per chain can be provided.

According to one advantageous feature of the present invention, thenumber of segments and/or chain links can also be recorded via sensors.In a circulating chain, this is done by the chain segments and/or chainlinks recorded by sensors between two consecutive runs of the localsignificance of the chain. When several structural changes to the chainare provided, the number of chain segments and/or chain links betweenthese local significances can be determined. Advantageously, the numbercan be determined from the number of recorded measured values.Alternatively, the number of chain segments and/or chain links can bespecified and stored, for example, in the memory of the sensor device.

According to one advantageous feature of the present invention, thesensors for detecting the local significance and the sensor forrecording the measured values from which the length values of the chainsegments and/or chain links are determined can be arranged at a fixedand known distance. Thus, a determined measured value or length value isassigned to the respective chain segment or chain link via the detectedposition of local significance and the number of measured valuesrecorded after detection of local significance (is optionally equal tothe passed chain segments or chain links).

According to one advantageous feature of the present invention, theelongation of the respective chain segment can be determined from themeasured values after the measured values have been recorded. Theselength values are then compared with a stored value. The stored valuecan be an absolute length value or the specification of a maximumpermissible deviation from an initial value. The initial value can bedetermined by the measurement during commissioning or it can also bepreset. The length values can then be stored optionally.

According to another aspect of the present invention, a sensor devicefor determining a length of a segment of a chain, includes a firstsensor configured to record measurement data to determine a position ofthe segment of the chain, and/or a second sensor configured to recordmeasurement data to determine a length value of the segment of thechain.

This ensures that measured values belonging to a chain segment can alsobe assigned to it. This is important to ensure a chain segment that isovercritically elongated can be identified and replaced if necessary.The length value of a segment is a value that allows conclusion as towhether and/or to what extent the length of the respective segment haschanged in comparison to a given value or a so-called zero measurement.The term “length value” relates to both absolute and relative values.

According to one advantageous feature of the present invention, thefirst and second sensors can be identical. This has the advantage thatonly one sensor is required to acquire both pieces of information. Thissaves costs compared to a solution with two sensors. In a further designaccording to the invention, the sensor for recording measurement data todetermine the elongation of a chain segment and/or the sensor forrecording measurement data to determine the position of a chain segmentis either a sensor for measuring the electrical and/or magneticproperties of the chain or the reluctance, an imaging sensor or anoptical sensor.

According to one advantageous feature of the present invention,provision can be made for a control unit configured to control at leastone of the first and second sensors and to record and process themeasurement data captured by the first sensor to determine an elongationof the segment of the chain and/or the measurement data captured by thesecond sensor. The control unit assigns the length values determinedfrom the measurement data to the corresponding chain segment. The lengthvalues of the respective chain segment of the chain and/or the positionof the respective chain segment within the chain can then be determinedfrom the measurement data.

According to still another aspect of the present invention, a chainincludes a plurality of chain links, a plurality of segments formed bythe chain links, and a local significance detectable by a sensor.

According to one advantageous feature of the present invention, thelocal significance can involve a local structural characteristic. Thelocal significance indicates a single chain segment and/or chain linkcompared to a multitude of other chain segments and/or chain linkslocated in the direct vicinity of the marked single chain segment orchain link. Advantageously, the chain can include several localsignificances.

According to one advantageous feature of the present invention, thelocal significance can be a strap fixed to a chain link. Other types ofattachment are also conceivable. Optionally, the local significance canalso be formed by a local change of a physical property of the chain.This can, for example, be a change of the magnetic field by a permanentmagnet fixed to a chain segment. Local significances are subject to thesole condition that they must be detectable by a sensor.

According to still another aspect of the present invention, a computerprogram for executing a method for acquiring and processing measurementdata of a sensor device is embodied in a non-transitory computerreadable medium and includes program instruction for controlling asensor for acquiring measurement data to determine length values ofsegments of a chain, program instruction for controlling a sensor foracquiring measurement data to determine a position of a segment of thechain, and program instruction for assigning specific length values tothe segments of the chain, respectively.

According to one advantageous feature of the present invention, thecomputer program can include program instruction for comparing thelength values determined from the measured values with a previouslystored comparison value. This reference value is a length value which,when reached or exceeded, no longer guarantees proper functionality ofthe chain. This comparison value is either determined by a separatemeasurement and/or stored in the control unit in which the computerprogram is executed.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the present invention will be morereadily apparent upon reading the following description of currentlypreferred exemplified embodiments of the invention with reference to theaccompanying drawing, in which:

FIG. 1 is a schematic illustration of a sensor device with two sensorunits for monitoring a closed chain drive in accordance with the presentinvention;

FIG. 2 a is a schematic illustration of a sensor device with two sensorunits for monitoring a chain running past the sensor device;

FIG. 2 b is a graphical illustration of signals of the two sensor unitsof FIG. 2 a;

FIG. 3 a is a schematic illustration of a sensor device with two sensorunits for monitoring a chain running past the sensor device inanticlockwise and clockwise rotation;

FIG. 3 b is a graphical illustration of signals of the two sensor unitsof FIG. 3 a for the chain passing in anticlockwise and clockwiserotation;

FIG. 4 a is a schematic illustration of a chain with chain segments withthe length of one chain link;

FIG. 4 b is a schematic illustration of a chain with chain segments withthe length of three chain link; and

FIG. 4 c is a schematic illustration of a chain with chain segments withthe length of six chain link.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Throughout all the figures, same or corresponding elements may generallybe indicated by same reference numerals. These depicted embodiments areto be understood as illustrative of the invention and not as limiting inany way. It should also be understood that the figures are notnecessarily to scale and that the embodiments may be illustrated bygraphic symbols, phantom lines, diagrammatic representations andfragmentary views. In certain instances, details which are not necessaryfor an understanding of the present invention or which render otherdetails difficult to perceive may have been omitted.

Turning now to the drawing, and in particular to FIG. 1 , there is showna schematic illustration of a sensor device, generally designated byreference numeral 1 and including two inductive proximity sensors 2, 3,which are arranged close to a closed chain 11. Chain 11 is guided aroundtwo sprockets 10 and has a large number of chain links 12. Three chainlinks 12 each form a chain segment 13. Sensor device 1 is located on theside of the load run 14 and opposite the side of the empty run 15. Thedistance d between the two inductive proximity sensors 2, 3 is selectedsuch that n+⅓ chain links 12 are located between the two sensors 2, 3.d=n*g+f  (1)

Here n describes the number of chain links 12 between the first sensor 2and the second sensor 3 and g the length of a chain link. In this designexample, f=⅓ was selected. When sensor device 1 is mounted on the loadrun 14, not only the elongation due to wear is measured but also theelongation due to load. In contrast, when sensor device 1 is mounted onthe empty run 15, only the elongation due to wear is measured.

FIG. 2 a shows a sensor device 1 with two sensor units 2, 3 formonitoring a chain 11 running past sensor device 1. The length of achain link 12 is indicated here by g and f is the partial length of achain link 12 by whose amount the second sensor 3 is displaced by aninteger multiple of the chain link length g compared to the first sensor2. In FIG. 2 b the signals A, B of sensors 2, 3 are shown. The chainlink length g is proportional to the time tp between two consecutivesignals of one of sensors 2, 3 and f is proportional to the time betweentwo consecutive signals of the first sensor 2 and the second sensor 3.When the chain is elongated, the clockwise direction of movement f_(r)or t_(Br) becomes smaller, and the anticlockwise direction of movementf_(l) or t_(Bl) becomes larger. The phase length of the frequencies ofsignals A and B of sensors 2, 3 is measured by measuring t_(B) andt_(p). The ratio t_(B)/(t_(p)*(n+t_(B))) in accordance withL/d=t _(B)(t _(p)*(n+t _(B)))  (2)is the speed-independent relation between chain segment length L and thesensor distance d. It is important that the sensor distance for a newchain 11 is selected so that f<0.5*g. It is assumed that the chain 11does not undergo an elongation greater than the length g of a half chainlink 12 within the selected sensor spacing d.

FIG. 3 a shows the conditions when the direction of chain travel changesfrom clockwise r to anticlockwise l. FIG. 3 b) shows the respectivesignals for clockwise and anticlockwise travel of chain 11. The ratio ofthe change in length ΔL of chain segment 13 to chain segment length ininitial state L₀ results from the following equation (3):ΔL/L ₀=(L _(x) −L ₀)/L ₀ =L _(x) /L ₀−1  (3).

With Lx as the length of chain segment 13 at the time of measurement.For clockwise circulating chain 11, length Lxr of chain segment 13results fromL _(xr) /d=n+t _(pxr)/(n+t _(pxr) +t _(Bxr))  (4),wherein t_(pxr) is the time interval between two successive signals A, Bof one of sensors 2, 3 of clockwise circulating chain 11 in loaded stateand t_(Bxr) is the time interval between the signal A of the firstsensor 2 and the next following signal B of sensor 3 of the clockwisecirculating chain 11 in loaded state. Length L_(0r) of chain segment 13in initial state L_(0r) is obtained fromL _(0r) /d=n+t _(p0r)/(n+t _(p0r) +t _(Bor))  (5),wherein t_(pxr) is the time interval between two successive signals A, Bof one of sensors 2, 3 of clockwise circulating chain 11 in loaded stateand t_(Bxr) is the time interval between the signal A of the firstsensor 2 and the next following signal B of sensor 3 of clockwisecirculating chain 11 in initial state of chain 11.

According to equation (3), the ratio of the change in length ΔL_(r) tooutput length L_(0r) of chain segment 13 for clockwise circulating chain11 results fromΔL _(r) /L _(0r)=(t _(B0r) /t _(p0r) −t _(Bxr) /t _(pxr))/(n+t _(Bxr) /t_(pxr))  (6).

For clockwise circulating chain 11, length L_(xl) of chain segment 13results fromL _(xl) /d=(n+1)+t _(pxl)/((n+1)+t _(pxl) +t _(Bxl))  (7),wherein t_(pxl) is the time interval between two successive signals A, Bof one of sensors 2, 3 of the anticlockwise circulating chain 11 inloaded state and t_(Bxl) is the time interval between the signal A ofthe first sensor 2 and the next following signal B of sensor 3 of theanticlockwise circulating chain 11 in loaded state. Length L_(0r) ofchain segment 13 in initial state L_(0l) is obtained for anticlockwisecirculating chain 11 fromL _(0l) /d=(n+1)+t _(p0l)/((n+1)+t _(p0l) +t _(B0l))  (8).

According to equation (3), the ratio of the change in length ΔL_(r) tooutput length L_(0r) of chain segment 13 is obtained for anticlockwisecirculating chain 11 fromΔL _(t) /L _(0l)=(t _(Bxl) /t _(pxl) −t _(B0l) /t _(p0l))/((n+1)−t_(Bxl) /t _(pxl))  (9).

FIG. 3 b shows the signals A and B of sensors 2 and 3 for a clockwisecirculating chain 11 and for an anticlockwise circulating chain 11. Inthis design example, f=⅓ was selected. For clockwise circulating chain11, t_(Br)/t_(pr)=0.33. If chain 11 runs in reverse, the value jumps tot_(Bl)/t_(pl)=1−0.33=0.67. The direction of the chain movement can thusbe clearly determined and ambiguities for the ratio t_(B)/t_(p) areexcluded. Consequently, the distance between sensors 2 and 3 must beselected so that f is ≠0 and f is ≠0.5. For a ratio t_(B)/t_(p)<0.5,equation (6) is used to calculate the elongation of chain 11. If theratio t_(B)/t_(p)>0.5, the elongation of chain 11 is calculated fromequation (9). The operating conditions for the sensor device are suchthat the sensor distance must not be so large that chain 11 in thesection between the sensors is not elongated more than ΔL=f*g. Atf=0.25*g, this corresponds to a maximum elongation ΔL_(max) ofΔL_(max)=0.25 for 10 chain links 12 and a maximum elongation ΔL_(max) ofΔL_(max)=2.5% for 100 chain links 12.

In FIGS. 4 a to 4 c , chains 12 with chain segments of varying lengthsare shown. For the chain in FIG. 4 a , the length of a chain segmentL_(s) at L_(s)=g. The chain in FIG. 4 b shows a chain 11 with a chainsegment length L_(s) of L_(s)=3*g, while in FIG. 4 c a chain with achain segment length L_(s) with L_(s)=6*g is shown.

An endless conveyor chain 11 with 7020 chain links 12 (16B chainaccording to ISO 606) used in food production is divided into 390 chainsections (design example 1). A chain section comprises 18 chain links12, whereby each of the 18 links has a conveying strap arranged on chain11, i.e. a chain section comprises 18 chain links 12 and a conveyingstrap. Chain links 12 have a length of g=2.54 cm according to ISO 606.To detect the position of chain 11, a magnet is fixed on the outer strapas a local significance. Alternatively, the magnet could also bearranged on the plug-in strap. To detect the change in length of chainsegments 13 during operation of chain 11, a chain condition monitoringcontrolled (CCM controlled) sensor device 1 based on reluctance sensorswas arranged in the immediate vicinity of chain 11. The position ofchain 11 is also monitored by means of a Hall sensor 2, 3. This isconnected via the controller to a display on which the position of thedefective chain segment 13 is displayed in case of a correspondingmeasurement result. During monitoring, measured values are recorded forall chain links 12 with regard to their change in length. At a chainspeed of 0.1-0.2 m/s, this results in a time interval of 0.15-0.25 sbetween two consecutive measurements. For this purpose, the change inlength of chain segments 13 in comparison to the initial length of chainlinks 12 is determined in %. To determine the position of chain 11, aperformance map of the individual graduations is created andcontinuously updated. Subsequently, chain 11 must be counted manually orthe machine moves to the affected chain link 12 with an appropriatecontrol routine. A marking on the chain is used to assign the measuredvalues to the individual chain links 12. During the measurement, eachchain link passing sensors 2, 3 is measured. The values determined arecompared with a reference value. The reference value is stored in theCCM memory. Alternatively, the reference value can also be transmittedwirelessly via the CCM monitor or via I/O link to the programmable logiccontroller (PLC).

In a second design example, an endless chain applied in food productionis used as in design example 1 described above. In contrast to designexample 1 described above, only 390 measuring positions per chaincirculation are provided here—one per chain section, whereby the chainsection comprises 18 chain links and a conveying strap. Such a chainsection corresponds to exactly one chain segment here. As a result, thechange in length is not determined here for each chain link 12 asdescribed above but only for the 390 chain segments 13. At a chain speedof 0.1-0.2 m/s, this results in a time interval of 2.3-4.5 s between twoconsecutive measurements. When detecting a critical length value for oneof these chain segments 13, only chain segment 13 with 18 chain links 12and one conveying strap must be replaced. It is advisable to select thelength of chain segment 12 so that it comprises the same elementsregardless of its position in chain 11. This ensures that there is ahigh degree of identical parts when selecting the required spare parts,which makes servicing much easier, as no knowledge of the type ofdefective component is required.

In another application example (design example 3), an endless chain 11with 3150 chain links 12 is used. This is a chain 11 of type 10B-1according to ISO 606. In initial state, the chain links 12 have a lengthof 15.875 mm (nominal pitch). Each outer link is provided with a gripperelement. A chain segment length of two chain links 12 is provided forwear monitoring. The number of chain segments 13 is therefore 1575. Amagnet is arranged on an outer strap to determine the chain position.Alternatively, the magnet could also be arranged on the plug-in strap.To determine the length values of the chain segments 13, aCCM-controlled sensor device 1 on the basis of reluctance sensors 2, 3is used, which detects the position of the outer strap of the chainequipped with the magnet to the CCM-controlled sensor device 1 via aHall sensor 2, 3. During monitoring of chain 11, all measured values foreach chain link 12 are recorded. At a chain speed of 0.6-0.8 m/s, thisresults in a time interval of 0.2-0.3 s between two consecutivemeasurements. For this purpose, the change in length of chain segments13 in comparison to the initial length of chain links 12 is determinedin %. The nominal pitch is specified according to ISO 606 and stored asa reference value. To determine the position of chain 11, a performancemap of the individual pitches is created and continuously updated.Subsequently, chain 11 must be counted manually or the machine moves tothe affected chain link 12 with an appropriate program. The assignmentof the length values to the individual chain links 12 is made via thedirection of movement of chain 11 and the number of determined lengthvalues after the magnet attached to the outer strap has passed throughHall sensor 2, 3.

The fourth application example describes a chain 11 for a liftingapplication with change of rotational direction. Unlike the previousexamples, this is not an endless chain 11. The 20B-2 chain 11 has chainlinks 12 with a nominal pitch (length of a chain link 12) of 31.75 mm inaccordance with ISO 606 231. The length of chain segment 13 is also31.75 mm, since a length value is assigned to each chain link 12. Amagnet is arranged on an outer strap to determine the position of chainlink 12 marked by the magnet in relation to sensor 2, 3 to detect thelength values. The length values are detected by a CCM-controlledreluctance sensor device and the position of chain 11 to theCCM-controlled reluctance sensor device 1 via the detection of themagnet by a Hall sensor 2, 3. For each chain link 12 passing through theCCM-controlled reluctance sensor device 1, a measured value is recordedfrom which the current length or the percentage deviation of the lengthof the respective chain link 12 from the nominal pitch is determined. Todetermine the position of chain 11, a performance map of the individualpitches is created and continuously updated. At an average chain speedof 0.6 m/s, one measurement value is recorded every 0.05 s.

While the invention has been illustrated and described in connectionwith currently preferred embodiments shown and described in detail, itis not intended to be limited to the details shown since variousmodifications and structural changes may be made without departing inany way from the spirit and scope of the present invention. Theembodiments were chosen and described in order to explain the principlesof the invention and practical application to thereby enable a personskilled in the art to best utilize the invention and various embodimentswith various modifications as are suited to the particular usecontemplated.

What is claimed is:
 1. A method for determining an elongation ofsegments of a chain of a chain drive during operation, said methodcomprising: recording a plurality of measured values at differentpositions of the chain with a first sensor and a second sensor arrangedat a defined distance from each other; determining a plurality of lengthvalues of the segments of the chain from the plurality of measuredvalues based on the defined distance, a time interval between twosuccessive signals of one of the first and second sensors, and a timeinterval between a signal of the first sensor and a next followingsignal of the second sensor; assigning the plurality of determinedlength values to the segments of the chain, respectively, wherein alength of the segments of the chain is smaller than a length of thechain; monitoring segments of the chain; identifying elongated segmentsof the chain by comparing the plurality of length values with storedvalues; and replacing only the identified elongated segments of thechain.
 2. The method of claim 1, wherein at least 5 of the segments aredistributed over the length of the chain.
 3. The method of claim 1,wherein a number of the segments corresponds to a number of chain linksof the chain which are guided past one or more sensors as the measuredvalues are recorded during operation.
 4. The method of claim 1, whereina measurement for recording the measured values is continuously repeatedduring operation of the chain drive.
 5. The method of claim 1, wherein achange in length values is determined from a comparison with a referencemeasurement or reference value.
 6. The method of claim 1, furthercomprising detecting a position of the segments of the chain.
 7. Themethod of claim 6, wherein a local significance of the chain isdetermined for detecting the position of the segments of the chain. 8.The method of claim 7, wherein the local significance includes astructural change in the chain.
 9. The method of claim 8, wherein thestructural change of the chain comprises a strap fixed to the chainand/or a permanent magnet fixed to the chain.
 10. The method of claim 7,further comprising assigning the determined length values to individualsegments of the chain on the basis of the position of the segments ofthe chain and/or the position of the determined local significance inthe chain.
 11. The method of claim 1, wherein a number of measuredvalues determined is at least equal to a number of segments of the chainor greater than a number of segments of the chain.
 12. The method ofclaim 1, wherein a number of segments of the chain is acquired from themeasured values.
 13. A system for determining an elongation of segmentsof a chain of a chain drive during operation, said system comprising: achain, said chain comprising: a plurality of chain links; a plurality ofsegments formed by the chain links; a local significance detectable by asensor device; and a sensor device for determining a length of a segmentof the chain, said sensor device comprising: a first sensor configuredto record measurement data to determine a position of the segment of thechain, and/or a second sensor arranged at a defined distance from thefirst sensor. said second sensor configured to record measurement datato determine a length value of the segment of the chain, said sensordevice further comprising a control unit configured to control at leastone of the first and second sensors and to record and process themeasurement data captured by the first sensor to determine an elongationof the segment of the chain and/or the measurement data captured by thesecond sensor based on the defined distance, a time interval between twosuccessive signals of one of the first and second sensors, and a timeinterval between a signal of the first sensor and a next following ofthe second sensor.
 14. The chain of claim 13, wherein the localsignificance is a local structural characteristic.
 15. The chain ofclaim 13, wherein the local significance is a local change in a physicalproperty of the chain.
 16. A computer program for executing a method foracquiring and processing measurement data of a sensor device, saidcomputer program embodied in a non-transitory computer readable mediumand comprising: program instruction for controlling a first sensor foracquiring measurement data to determine length values of segments of achain; program instruction for controlling a second sensor for acquiringmeasurement data to determine a position of a segment of the chain;program instruction for determining the length values based on a defineddistance between the first sensor and the second sensor, a time intervalbetween two successive signals of one of the first and second sensors,and a time interval between a signal of the first sensor and a nextfollowing signal of the second sensor; program instruction for assigningthe determined length values to the segments of the chain, respectively;program instruction for monitoring segments of the chain; and programinstruction for identifying elongated segments of the chain that need tobe replaced by comparing the determined length values with storedvalues.
 17. The computer program of claim 16, wherein the first andsecond sensors are identical.